The latest SAMtools 1.14 has removed some old files from the build as explained here
This updated EasyBlock addresses these changes.
I tested it as low as SAMtools-1.10-GCC-9.3.0.eb and that seems to have worked, after putting self.lib_files [] in the right line.

Test report by @boegel

Overview of tested easyconfigs (in order)

• SUCCESS SAMtools-1.10-GCC-9.3.0.eb
• SUCCESS SAMtools-1.11-GCC-10.2.0.eb
• SUCCESS SAMtools-1.11-GCC-9.3.0.eb
• SUCCESS SAMtools-1.12-GCC-10.3.0.eb
• SUCCESS SAMtools-1.12-GCC-9.3.0.eb
• SUCCESS SAMtools-1.13-GCC-10.3.0.eb

Build succeeded for 6 out of 6 (6 easyconfigs in total)
node3501.doduo.os - Linux RHEL 8.2, x86_64, AMD EPYC 7552 48-Core Processor (zen2), Python 3.6.8
See https://gist.github.com/db472722b2ccd1934b002389de4868c5 for a full test report.